[flurp]

EDIT: I found better documentation on this.

Some US states require ID.

> The person approached is not required to identify himself or answer any other questions, and may leave at any time

From http://en.wikipedia.org/wiki/Stop_and_identify_statutes#Stat...

http://www.quora.com/In-the-US-under-what-situations-are-you... --old:

Depends. A quick google found this: http://www.flexyourrights.org/faqs/when-can-police-ask-for-i...

> As of 2013, 24 states had stop-and-identify laws. Regardless of your state’s law, keep in mind that police can never compel you to identify yourself without reasonable suspicion to believe you’re involved in illegal activity

[sukilot]

No states require an ID card. Some states require you to provide ID information, and may detain you as long as necessary to determine your identidy. Thus detainment is often used as an unofficial punishment for not providing an ID card.